This invention relates to a post processing apparatus which receives sheets having images formed by an image forming apparatus such as printers, copy machines or copiers and carries out post processing like stapling, punching or stamping on the sheets, and relates to a sheet aligning apparatus which positions the sheets on the post processing apparatus at a predetermined position.
In general, this kind of sheet aligning apparatus has been broadly known as an apparatus, which sets sheets having images formed by the image forming apparatus at a predetermined position on a tray, performs on the stack of the sheets post processing such as stapling, stamping, punching or others, and stores them to a storing stacker in a downstream side. Accordingly, the process tray necessitates a sheet aligning mechanism for performing regular alignments on a stage of carrying out the post-processing to the sheets.
This kind of sheet aligning apparatus has conventionally been disclosed in, for example, Japanese Patent Application Publication No. 2003-128332. This publication document prepares set-copies by piling the sheets delivered out of the image forming apparatus on the process tray from a sheet outlet. The stack of each set is stitched by a staple device disposed at the process tray, and the stitched sheet stack is delivered to a storing tray arranged at the downstream of the process tray.
Therefore, the process tray is equipped with reciprocally delivering rollers, conveys the sheets from the sheet outlet to the downstream side along the process tray, reversely rotates the delivering rollers after the sheets have been guided at their backward ends on the process tray, and switches back the sheets thereon.
The process tray is furnished with a restraining stopper for pushing the sheets at their back ends thereto in order to regulate to position the sheets. Although not illustrating in the Patent Publication Document, the process tray is provided with a sheet width regulating plate for positioning the sheets at their one-sides to a standard position.
With this structure, the sheets from the sheet outlet are piled on the process tray to carry out the set-copies justification, and at the same time, the sheets are aligned at the predetermined position.
When piling to align the sheets on the process tray as mentioned above, there have conventionally been arranged with conveyor means for moving the sheets in a conveying direction and aligning means for moving the sheets in a direction crossing conveying.
The aligning means include an alignment plate which moves by engaging rotors such as a roller or the sheets at their ends.
Therefore, conventionally, the sheets delivered on the process tray are moved by the conveying means toward a restraining stopper, at the same time, moved by the aligning means in the direction perpendicular to the conveying direction crossing by the conveying means, and set for positioning to the restraining stopper.
Since a prior art actuates the conveying means and the aligning means on the sheets concurrently, the prior art has a problem of causing bent at a corner of a sheet or skew, when colliding with the restraining stopper.
This condition is illustrated in FIG. 11, and the conveying force F1 acts in a conveying direction (the shown direction is opposite to a sheet discharge direction) by a first conveying means 50, and at the same time, the conveying force F2 acts in a direction crossing the conveying direction by an aligning means 51. When the sheets concurrently effected with the conveying force F1 and F2 collide with the restraining stopper 52, reaction F3 is generated in the illustrated oblique lines from the restraining stopper. This reaction F3 acts on the sheets as a manner of balancing the conveying force F1 and F2.
In case, therefore, resultant force of the conveying forces F1 and F2 is large, reaction F3 balanced therewith is also large. As a result, the sheets are bent at the illustrated oblique part and it causes the bent sheet ears.
When the sheet bent at a corner occurs in the sheet, the sheet is skewed as a whole, and this skew affects the post process such as the staple binding.
In particular, if the sheet sizes are different in width as shown and in case of the large sized sheet La, the reaction F3 acts over the large area of the slash portion La1 by the above mentioned conveying forces F1 and F2, while in case of the sheet Lb of the small size, the reaction F3 acts in the small area of the slash portion. Accordingly, when designing the apparatus, if the conveying forces F1 and F2 are determined in response to the sheet La of the large size, the sheet bent at the corner easily occurs in case the sheets have the small size.
Contrary thereto, when designing the apparatus, if the conveying forces F1 and F2 are determined in response to the sheet of the small size, the large sized sheets do not receive the conveying force and are not completely sent, resulting in positioning under a resist condition.
In the present invention, therefore, it is an object to provide a sheet aligning apparatus which neither causes corner edge-bending or skewing at the sheet ends when pushing the sheets to regulate them on the process tray by colliding the sheets with the restraining member, and at the same time, nor regulate the sheets under the condition of creating the resist condition or non-reaching portions of the sheet end to the restraining stopper.
Further, it is another object to provide a post processing device which enables to perform the post process to the right position of the sheet when carrying out the post process to the sheets piled on the process tray, and provide an image forming apparatus having the post processing device.
Further objects and advantages of the invention will be apparent from the following description of the invention.